Put the water softener into the "bypass" mode and see if the noise stops. The noise is usually caused by either a water softener or a pressure reducing valve on the main line into the house.

: I'm in search of a answer to why water pipes would moan after you turn the water off. The noise started about a month ago,and it's quite loud. My children are scared when they here it and my wife keeps pestering me about it.: The water comes into the house through the basement to the water softner and the pipes vibrate when the moaning starts. I would be forever grateful if you had a idea whats is causing it.: : Thanks